Communication control unit and communication control method applied for multicast-supporting LAN

ABSTRACT

A multicast processing section constructs, when it is determined that a received packet is a packet on a multicast packet and multicast group management protocol, a table showing a correlation between a host device and a multicast group in a port number-multicast physical address correlation storing section as well as in a multicast router-connected port storing section according to the received packet, and controls to transfer a packet for each multicast group between a multicast router and host devices according to the table.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/191,761, filed on Jul. 9, 2002, now U.S. Pat. No. 7,487,251 B2 whichis a continuation of U.S. application Ser. No. 09/170,663, filed on Oct.13, 1998, now U.S. Pat. No. 6,457,059 B1.

FIELD OF THE INVENTION

The present invention relates to a communication control unit forcontrolling a port to be used, for example, when a packet is transferredby using a multicast-supporting LAN (Local Area Network) as well as to acommunication control method applied for a multicast-supporting LAN.

BACKGROUND OF THE INVENTION

In association with rapid and widespread use of personal computers inrecent years, LAN has also become increasingly common, while computersand networks themselves have been more advanced and more powerful. Inaddition, wide use of WWW (World Wide Web) as well as of multimedia datasuch as moving images and voice is progressing, and the traffic ofnetworks is more and more increasing, so that introduction of networkrepeater such as a communication control unit and a high speed router,for example, a switching hub allowing large amounts of data to betransmitted with high speed to a network is progressing. Further, datatransfer based on a multicast technology has been started as atechnology for efficiently transferring large amounts of data, and itmay be estimated that the widespread use of data transfer using amulticast is more and more increasing from now on.

Description is made hereinafter for a multicast-supporting LAN in whicha conventional type of communication control unit is applied. FIG. 15 isa view showing a construction of the conventional type ofmulticast-supporting LAN. The multicast-supporting LAN shown in FIG. 15comprises multicast routers 1001 and 1002 for relaying data transferusing a multicast according to an IP address; communications controlunits 1101, 1102, and 1103 for switching input/output of a packet withdata to be transferred according to MAC addresses; a hub 1201functioning as, for example, a multi-port transceiver; and host devices1301-1307 each functioning as a terminal. The network construction shownin FIG. 15 is a part of a LAN taken out to describe the network based onthe conventional technology.

FIG. 16 and FIG. 17 are views for explaining a general outline of anoperation of IGMPv2 (Internet Group Management Protocol Version 2), FIG.16 shows a sequence for a host device to become a member of a multicastgroup, and FIG. 17 shows a sequence for a host device to leave amulticast group. It should be noted that FIG. 16 and FIG. 17 show aconstruction obtained by taking out a part with the multicast router1001 and host devices 1304 and 1305 from the construction in FIG. 15.

At first, description is made for a method of becoming a member of amulticast group with reference to FIG. 16. It is assumed here that thehost device 1305 desires a member of a multicast group, and descriptionis made for the operation within a range of the construction shown inFIG. 16 to make description simpler. The multicast router 1001periodically transmits a query message (Host Membership Query) to adestination with the IP address 224.0.0.1 (All-Systems-Group) to ask thehost devices 1304 and 1305 each connected to a local network to become amember of one of multicast groups and to find out where the desiredmulticast group exists.

In this case, the host device 1305 having a desire of becoming a memberof a multicast group transmits a report message (Host Member Report) toa multicast address of a group hoping to become a member to report themulticast address of which the host device desires a member in responseto the received a query from the multicast router 1001.

At this point of time, the host device 1305 trying to transmit a reporttransmits the report at a random time during a period of time until aMax Response Time (Default: 10 sec) included in the query message iselapsed. If there are a plurality of other host devices each to send areport to the same group as that the report to be sent to, the multicastrouter receives a first transmitted report by one of host devices, sothat the other host devices do not transmit the report. Namely, when aplurality of host devices in a network medium are connected to sharedmedia, only one report for each multicast group is transmitted.

The multicast-supporting router 1001 receives the report, finds out amulticast group of which the host device 1305 desires a member, andstarts to transmit, if it is found where a multicast for the multicastgroup exists, multicast data to a local network based on a multicastrouting protocol.

Next description is made as to a method of leaving a multicast groupwith reference with FIG. 17. It is assumed here that the host device1305 desires to leave a multicast group, and description is made for theoperation within a range of the construction shown in FIG. 17 to makedescription simpler. The host device 1305 desiring to leave themulticast group of which the device is a member transmits a leavemessage to the IP address 224.0.0.2 (All-Routers-Group) at the point oftime when leaving is decided.

The multicast router 1001 having received the leave transmits a GS query(Group Specific Query) message to the multicast group address to checkwhether any other host devices each being a member of the multicastgroup exist or not. If there are some host devices each as a member ofthe multicast group other than the host device having transmitted theleave, the host device 1305 transmits a report to the multicast router1001 to convey the existence thereof.

Herein, although there is also Version 1 of IGMP (defined in RFC1112),IGMPv2 supports compatibility with IGMPv1, so that any host device androuter supporting Version 1 may exist in a local network. Leave is amessage added in IGMPv2, namely, in Version 1, a multicast router findsout existence or leaving of a receiving host device depending onpresence or absence of a response with a report to periodicaltransmission of a query.

Conventionally, unicast physical addresses of terminals each connectedto each port are stored in a communication control unit such as aswitching hub, and high speed packet transfer of a unicast packet havinga unicast physical address of a terminal or of a broadcast packet toterminals is realized only to a target port or target ports based on ahardware switching technology.

As for a multicast packet used for multimedia data transfer, however, itis difficult to discriminate a plurality of particular ports requiringthe multicast packet from others as compared to the case of unicast, andfor this reason, a multicast packet is not transferred only to portsrequiring the multicast packet but is transferred to all ports like thebroadcast packet.

The multicast packet as described above has in many cases continuousstream data as well as a large amount of data with a data type of movingimages and other data, which causes limitations of processing by thecommunication control unit, and for this reason, there occurinconveniences such that a disposal rate of multicast packets becomeshigher, a transfer delay time becomes longer, or a bad influence isgiven to transfer of other unicast packet.

Although there is a device for performing message transaction with amulticast router connected to a network using a particular protocol totransfer a multicast packet only to a port of a required communicationcontrol unit, the operation of transferring a multicast packet only to arequired particular port can not be realized unless the multicast routersupporting the particular protocol is combined with the communicationcontrol unit.

In the multicast-supporting LAN described above, there is acommunication control unit which packages IGMP as a management protocolof a multicast group between a multicast router and host devices on itsown, but a merit such that a LAN switch by nature realizes high speeddata transfer by forwarding a data packet in a data linked layer may belost.

When a particular protocol specific to a device is used, connectivitybetween makers or devices can not be ensured.

It is an object to provide, to solve the problems described above, acommunication control unit which can realize efficient transfer formulticast as well as unicast data transfer by transferring multicastdata only to required ports with the existing protocol and networkconstruction as well as a communication control method applied for amulticast-supporting LAN.

With the present invention, when it is determined that the receivedpacket is a packet on a multicast as well as multicast group managementprotocol, a table showing a correlation between the host devices andmulticast groups is constructed according to the received packet, andpacket transfer for each multicast group between the multicast routerand host devices is controlled according to the table, so that amulticast packet can be multicast-transferred only to required hostdevices with the existing protocol and network construction, and withthis feature, it is possible to realize efficient transfer for multicastas well as unicast data transfer.

With the present invention, when it is determined that the packet on themulticast as well as multicast group management protocol is a query, theport having received the packet on a query among a plurality of ports isregistered in the table as a port to which the multicast router isconnected, so that it is possible to update a correlation between a portand a multicast router as required according to contents of the packet.

With the present invention, when a packet on a query is received, it iscontrolled to transfer the packet to all the ports other than the porthaving received the received packet among the plurality of ports, sothat the query can surely be transferred to devices under controls by amulticast router.

With the present invention, a ping is periodically transferred to theport to which the multicast router is connected among the plurality ofports by referring to the table, and when there is any port that doesnot respond to the ping, the correlation between the port and themulticast router is deleted from the table, so that it is possible toupdate disappearance of a correlation between a multicast router and aport as required according to contents of the packet.

With the present invention, when it is determined that the packet on themulticast as well as multicast group management protocol is a report,the port having received the packet on a report among the plurality ofports is registered in the table as a connecting port used when the hostdevice connected to the port is to be a member of an arbitrary multicastgroup, so that it is possible to update generation of a correlationbetween a port and a host device for each multicast group as requiredaccording to contents of the packet.

With the present invention, when a packet on a report is received, thepacket on a report is controlled to transfer only to the port to whichthe multicast router is connected by referring to the table, so that thereport from the host device can surely be transferred to the multicastrouter.

With the present invention, when it is determined that the packet on themulticast as well as multicast group management protocol is leave, theport having received the packet on leave among the plurality of ports isdeleted from the table regarding as a connecting port used when the hostdevice connected to the port leaves an arbitrary multicast group, sothat it is possible to update disappearance of a correlation between aport and a host device for each multicast group as required according tocontents of the packet.

With the present invention, when a packet on leave is received, thepacket on leave is controlled to transfer only to the port to which themulticast router is connected by referring to the table, so that theleave from the host device can surely be transferred to the multicastrouter.

With the present invention, when a packet on leave is received, thepacket on leave is controlled to transfer to all the ports other thanthe port having received the packet on leave among the plurality ofports, so that the need for processing of searching a port to which themulticast router is connected is eliminated, and with this feature, itis possible to make low speed processing of leave faster by reducing aload to the processing at the time of leave operation.

With the present invention, when a packet on a group specific query forchecking that there is no host device being a member of a multicastgroup is received, the packet on a group specific query is controlled totransfer, by referring to the table, to ports each to which a multicastrouter is connected other than the port connecting thereto the hostdevice having been a member of a multicast group as well as the porthaving received the packet on a group specific query, so that the groupspecific query does not need to be broadcast, and with this feature, itis possible to efficiently check that there is no host device havingbeen a member of a multicast group.

With the present invention, when a packet on a group specific query isreceived, the packet on a group specific query is controlled to transferto all the ports other than the port having received the packet on agroup specific query among the plurality of ports, so that the need forprocessing of searching a port to which the multicast router isconnected is eliminated, and with this feature, it is possible to makeprocessing of transferring the group specific query faster by reducing aload to the processing at the time of group specific query operation.

With the present invention, when there is any port from which a reportis not responded within a specified period of time after the packet on aquery is received, the correlation between the port and the host deviceis deleted from the table, so that it is possible to update informationthat becomes nothing to do with multicast packet transfer as required,and with this feature, the processing can efficiently be executed.

With the present invention, an update operation of the table is executedunder controls by the external device, so that a load to thecommunication control unit itself can be reduced.

With the present invention, when a packet is received by a portconnected to the multicast router, and if the received packet is amulticast packet, the received packet is transferred to the host devicesbelonging to the multicast group by referring to the table, so that asequence of checking the multicast group management protocol can beomitted, and with this feature, forwarding of a multicast packet can bemade faster.

With the present invention, when a packet is received by a portconnected to a host device belonging to a multicast group stored in thetable, and if the received packet is a multicast packet, the receivedpacket is transferred to the multicast router belonging to the multicastgroup by referring to the table, so that a sequence of checking themulticast group management protocol can be omitted, and with thisfeature, forwarding of a multicast packet can be made faster.

With the present invention, when a packet is received by a port to whichthe router is connected, and if the received packet is a multicastpacket, the received packet is transferred to the multicast router byreferring to the table, so that it is possible to ensure the operationof a multicast routing protocol on the network comprising a plurality ofmulticast routers and a plurality of switching hubs.

With the present invention, when the packet on the multicast as well asmulticast group management protocol is a query to ask a host device tobecome a member of a multicast group, only a first report in eachmulticast group among reports each having a desire to become a member ofa multicast group received by each of the ports is transferred to acorresponding port to which the multicast router is connected byreferring the table during the specified period of time preset insidethe query, and the following reports are disposed after the specifiedperiod of time is elapsed, so that overlaps of reports to a multicastrouter can be avoided from their transmission even on a network in whichthe subnet comprises a large number of switching hubs and host devicesdesiring reception of multicast data are connected to a large number ofports of each of the switching hubs.

With the present invention, even when it is determined that the receivedpacket is a packet on a multicast as well as multicast group managementprotocol, but if the received packet does not correspond at least to anytype of a query to ask a host device to become a member of a multicastgroup, a report that a host device desires to be a member of a multicastgroup, and of leave indicating that a host device desires to leave amulticast group, the received packet is transferred to all the pluralityof ports, so that when it can not be determined which type a multicastpacket corresponds to, the determination can be left to each device as adestination to which the packet is transferred.

With the present invention, even when it is determined that the receivedpacket is a packet on the multicast as well as multicast groupmanagement protocol, but if the received packet does not correspond atleast to any type of query to ask a host device to become a member of amulticast group, a report that a host device desires to be a member of amulticast group, and of leave indicating that a host device desires toleave a multicast group, the received packet is disposed, so that anunclear type of multicast packet is cleared off from a network, whichallows ordinary multicast packet transfer to be more efficient.

With the present invention, there are steps of determining contents of areceived packet, and constructing, when it is determined that thereceived packet is a packet on the multicast as well as multicast groupmanagement protocol, a table showing a correlation between the hostdevices and multicast groups for controlling a path of a multicastpacket according to the received packet, so that conditions to controlmulticast-transfer of a multicast packet only to required host deviceswith the existing protocol and network construction can be maintainedinside the packet.

With the present invention, there is also a step of transferring, when amulticast packet is received from the multicast router, a packet foreach multicast group between the multicast router and host devicesaccording to the table showing a correlation between host devices andmulticast groups, so that a multicast packet can bemulticast-transferred only to required host devices with the existingprotocol and network construction, and with this feature, it is possibleto realize efficient transfer for multicast as well as unicast datatransfer.

Other objects and features of this invention will become understood fromthe following description with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing one example of constructing amulticast-supporting LAN in which the communication control unitaccording to one embodiment of the present invention is applied;

FIG. 2 is a block diagram functionally showing the communication controlunit according to one embodiment of the present invention;

FIG. 3 is a block diagram showing the hardware of the communicationcontrol unit according to one embodiment of the present invention;

FIG. 4 is a view showing an example of contents stored in a portnumber-multicast physical address correlation stored table;

FIG. 5 is a view showing an example of contents stored in a multicastrouter-connected port number stored table;

FIG. 6 is a view for explaining an IGMP packet on Ethernet;

FIG. 7 is a view showing a format of an IGMP message packet;

FIG. 8 is a view showing a format of an IP header;

FIG. 9 is a view showing a format of an IGMP Version 1 message;

FIG. 10 is a view showing a format of an IGMP Version 2 message;

FIG. 11 is a view showing a structure of a MAC header in the case ofEthernet;

FIG. 12 is a view showing a structure of a ping packet;

FIG. 13 is a flow chart for explaining a main operation of acommunication control unit according to the embodiment;

FIG. 14 is a flow chart for explaining an operation at the time ofreceiving a query;

FIG. 15 is a view showing a construction of the conventional type ofmulticast-supporting LAN;

FIG. 16 is a view for explaining a sequence of taking part in amulticast group by a host device; and

FIG. 17 is a view for explaining a sequence of leaving a multicast groupby a host device.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Detailed description is made hereinafter for preferred embodiments of acommunication control unit and a communication control method appliedfor a multicast-supporting LAN with reference to the related drawings.

At first, description is made for a multicast-supporting LAN. FIG. 1 isa view showing one example of constructing the multicast-supporting LANin which the communication control unit according to one embodiment ofthe present invention is applied. The multicast-supporting LAN shown inthe figure shows a section of a subnet SB. This subnet SB comprises twounits of communication control unit 1A and 1B serially connected to eachother between multicast routers 11 and 12; host devices 21, 22, 23, and24 connected to the communication control unit 1A; and host devices 25,and 26 connected to the communication control unit 1B.

Herein, the multicast routers 11 and 12 are routers supporting IGMP as amulticast management protocol used for communications with the hostdevices. The host devices 21 to 26 are devices such as personalcomputers and work stations, and each has a function operable accordingto the IGMP. Therefore, existing devices are employed for the multicastrouters 11, 12 and the host devices 21 to 26.

Next detailed description is made for the communication control devices1A and 1B. The construction of the communication control unit 1A has thesame as that of the communication control unit 1B concerning functionsand hardware, so that description assumes hereinafter the constructionof the communication control unit 1A as a representative. FIG. 2 is ablock diagram functionally showing the communication control unit 1Aaccording to one embodiment of the present invention.

The communication control unit 1A comprises, as shown in FIG. 2, a portsection 2 for connecting thereto the host devices 21 to 24, multicastrouter 11, and the communication control unit 1B; a multicast processingsection 3 comprising a multicast-packet type determining/packetswitching section 4 for determining whether a packet received from theport 2 is a multicast packet or an IGMP message packet and processing asa determined type and an IGMP processing section 5 for processing anIGMP message; a packet switching section 6 for performing the samepacket transfer as that of the ordinary communication control unit; aport number-unicast address correlation storing section 7 for storingtherein a correlation between port numbers and unicast addresses; a portnumber-multicast address correlation storing section 8 for storingtherein a correlation between port numbers and multicast addresses; anda multicast router-connected port storing section 9 for storing acorrelation between multicast routes and connected ports.

Next description is made for hardware of the communication control unit1A functionally shown in FIG. 2. FIG. 3 is a block diagram showing thehardware of the communication control unit 1A.

The communication control unit 1A comprises, as shown in FIG. 3 as oneof examples, a port 101 corresponding to the port section 2 forperforming the function thereof; a multicast packet processing section102 as well as a report controlling timer 110 corresponding to themulticast processing section 3 for performing the function thereof; apacket type determining/forwarding section 103 corresponding to themulticast-packet type determining/packet switching section 4 forperforming the function thereof; an IGMP Leave message processingsection 104 corresponding to the IGMP processing section 5 forperforming the function thereof; a switching hub section 105corresponding to the packet switching section 6 for performing thefunction thereof; a port number-unicast address correlation stored table106 corresponding to the port number-unicast address correlation storingsection 7 for performing the function thereof; a port number-multicastaddress correlated memory 107 corresponding to the port number-multicastaddress correlation storing section 8 for performing the functionthereof; a table entry timer 111; a multicast router-connected portmemory 108 as well as a ping processing section 112 corresponding to themulticast router-connected port storing section 9 for performing thefunction thereof; and an external terminal interface 109.

The port 101 is divided, as one example, into seven port numbers.Connected to a port #1, taking up the subnet SN in FIG. 1 as an example,is the multicast router 11, the host devices 21, 22, 23, and 24 areconnected to ports #2, #3, #4, and #5 respectively, and thecommunication control unit 1B is connected to a port #7. It should benoted that a port #6 is not available.

In the multicast packet processing section 102, the packet typedetermining/forwarding section 103 comprises aunicast-broadcast/multicast packet determining section 201, aunicast-broadcast/multicast packet switching section 202, and an IGMPmessage determining/processing section 203. Theunicast-broadcast/multicast packet determining section 201 determineswhether a received packet is a unicast-broadcast packet or a multicastpacket.

The unicast-broadcast/multicast packet switching section 202 performspacket transfer according to a case of the unicast-broadcast as well asto a case of the multicast respectively. The IGMP messagedetermining/processing section 203 determines, when it is determinedthat the received packet is the multicast packet, a type of the IGMPmessage (query, report, leave) and executes processing according to thetype.

Here, a term “query” indicates a message transmitted to each host devicefrom a multicast router to ask the host device to become a member of amulticast group, and a term “report” indicates a message transmittedfrom a host device to a multicast router to desire a member of amulticast group. A term “leave” indicates a message transmitted from ahost device to a multicast router to desire leaving from the multicastgroup.

The IGMP Leave message processing section 104 comprises a multicastphysical address generating section 204. This multicast physical addressgenerating section 204 fetches an IP multicast address included in asection of an IGMP message on Leave, namely of a Leave message from theIGMP message determining/processing section 203, converts the address toa multicast MAC address, and deletes a corresponding correlation betweena port number and a multicast MAC address of the port number-multicastaddress correlated memory 107. The report control timer 110 is connectedto the IGMP message determining/processing section 203, and measures,when a received packet is a query, a Max Response Time set in the queryat the point of time when the query is received.

The switching hub section 105 and the port number-unicast addresscorrelation stored table 106 realize a function as a switching huboperating in an ordinary communication control unit. Namely, when it isdetermined in the unicast-broadcast/multicast packet determining section201 that the received packet is a unicast packet or broadcast packet,the packet for unicast or broadcast is sent to the switching hub 105through the unicast-broadcast/multicast packet switching section 202,and an ordinary switching operation is executed therein.

The port number-multicast address correlated memory 107 is a memory unitfor managing a correlation between each port number of the port 101 andmulticast address (each MAC address of host devices as members of themulticast group). This port number-multicast address correlated memory107 comprises a table-reading/writing/deleting control section 205, aport number-multicast physical address correlation stored table 206, anda table-writing/deleting control section 207.

The port number-multicast physical address correlation stored table 206stores therein a correlation between each port number of the port 101and multicast address (each MAC address of host devices as members ofthe multicast group) as a table. The table-reading/writing/deletingcontrol section 205 updates (read/write/update) the correlation on theport number-multicast physical address correlation stored table 206according to controls provided by the multicast packet processingsection 102.

The table-writing/deleting control section 207 deletes, when it ismeasured by a table entry timer 111 that a prespecified time or more haspassed for a time interval between a query and a report thereto, acorresponding correlation on the port number-multicast physical addresscorrelation stored table 206. The table entry timer 111 measures a timeinterval between a query and a report thereto in the correlation on theport number-multicast physical address correlation stored table 206.

The multicast router-connected port memory 108 is a memory unit formanaging a correlation between each port number of the port 101 andmulticast router address. This multicast router-connected port memory108 comprises a table-reading/writing/deleting control section 208, amulticast router-connected port number stored table 209, and atable-writing/deleting control section 210.

The multicast router-connected port number stored table 209 storestherein a correlation between each port number of the port 101 andmulticast router address as a table. The table-reading/writing/deletingcontrol section 208 updates (read/write/update) the correlation on themulticast router-connected port number stored table 209 according tocontrols provided by the multicast packet processing section 102.

The table-writing/deleting control section 210 deletes, when it ismeasured by the ping processing section 112 that a prespecified time ormore has passed for a time interval until a response to the ping is madeto the multicast router, a corresponding correlation (multicast routeraddress) on the multicast router-connected port number stored table 209.The ping processing section 112 measures a response time to a ping inthe correlation on the multicast router-connected port number storedtable 209.

Herein, the external terminal interface 109 works as an interfacebetween an external device connected thereto and the internal sections.Contents stored in the port number-multicast physical addresscorrelation stored table 206 as well as in the multicastrouter-connected port number stored table 209 can be updated with amanual by an external device connected to the external terminalinterface 109.

Next description is made for contents of the tables. FIG. 4 is a viewshowing an example of contents stored in the port number-multicastphysical address correlation stored table 206, and FIG. 5 is a viewshowing an example of contents stored in the multicast router-connectedport number stored table 209. Each of the stored contents in FIG. 4 andFIG. 5 follows the subnet SN shown in FIG. 1 respectively. FIG. 4 showsa correlation between port numbers and multicast MAC addresses. A numberof multicast MAC addresses as far as m-units (m: natural number) can beset to each of the port numbers. In the example of FIG. 4, one or moreof multicast MAC addresses are allocated to each of the port numbers 2,3, 4, 5, and 7.

Allocated to the port number 2 are two addresses of 01:00:5e:xx:xx:xxand 01:00:5e:zz:zz:zz as multicast MAC addresses. Accordingly, the hostdevice 21 is a member of two multicast groups. Allocated to the portnumber 3 is one address of 01:00:5e:yy:yy:yy as a multicast MAC address.

Accordingly, the host device 22 is a member of one multicast group.Allocated to the port number 4 is one address of 01:00:5e:zz:zz:zz as amulticast MAC address. Accordingly, the host device 23 is a member ofone multicast group.

Allocated to the port number 5 are two addresses of 01:00:5e:ww:ww:wwand 01:00:5e:zz:zz:zz as multicast MAC addresses. Accordingly, the hostdevice 24 is a member of two multicast groups. Allocated to the portnumber 7 are three addresses of 01:00:5e:zz:zz:zz, 01:00:5e:yy:yy:yy,and 01:00:5e:xx:xx:xx as multicast MAC addresses. Accordingly, the hostdevices 25 and 26 belonging to the communication control unit 1B aremembers of three multicast groups respectively.

In the multicast MAC addresses, the address 01:00:5e:xx:xx:xx isallocated to the port numbers 2 and 7, which indicates that the hostdevice 21 and the host devices belonging to the communication controlunit 1B are members of the common multicast group. The address01:00:5e:yy:yy:yy is allocated to the port numbers 3 and 7, whichindicates that the host device 22 and the host devices belonging to thecommunication control unit 1B are members of the common multicast group.

The address 01:00:5e:zz:zz:zz is allocated to the port numbers 2, 4, 5,and 7, which indicates that the host devices 21, 23, and 24 as well asthe host devices belonging to the communication control unit 1B aremembers of the common multicast group. The address 01:00:5e:ww:ww:ww isallocated only to the port number 5, which indicates that only the hostdevice 24 in the subnet SN is a member of this multicast group. Itshould be noted that all the reference signs X, Y, Z, W in the“xx:xx:xx”, “yy:yy:yy”, “zz:zz:zz”, and “ww:ww:ww” do not always showthe same number.

FIG. 5 shows a correlation between port numbers and multicast routerdetected or not/multicast router addresses. The number of multicastrouter addresses as far as m-units can be set to each of the portnumbers. In the example of FIG. 5, one or more of multicast routeraddresses are allocated to the port numbers 1 and 7. Connected to theport numbers 1 and 7 are the multicast router 11 with the addressaaa.aa.aaa.a and the multicast router 12 (through the communicationcontrol unit 1B) with the address bbb.bb.bbb.bbb respectively.

Accordingly, in the multicast router-connected port number stored table209, as shown in FIG. 5, “Connected to multicast router or not” is Yes,and “Multicast router address” is aaa.aa.aaa.a each corresponding to theport number 1, and “Connected to multicast router or not” is Yes, and“Multicast router address” is bbb.bb.bbb.bbb each corresponding to theport number 7. It should be noted that all the reference signs a and bdo not always show the same number.

Next description is made for a packet. Description below assumes a casethat a network media is Ethernet. FIG. 6 is a view for explaining anIGMP packet on Ethernet, FIG. 7 is a view showing a format of an IGMPmessage packet, FIG. 8 is a view showing a format of an IP header, FIG.9 is a view showing a format of an IGMP Version 1 message, FIG. 10 is aview showing a format of an IGMP Version 2 message, FIG. 11 is a viewshowing a structure of a MAC header in the case of Ethernet, and FIG. 12is a view showing a structure of a ping packet.

In mapping of multicast IP addresses and physical layer addresses, as inthe case shown in FIG. 6, a correlation between a multicast IP address(also called an IP address in Class D) and a physical address is definedin the standard (current one is RFC1700) that 23 bits in the low orderof an IP address of Class D should be put in 23 bits in the low order ofa multicast physical address “01.00.5E.00.00.00 (hexadecimal)”. Forexample, a multicast IP address “239.133.130.34 (hexadecimal)” is a MACaddress “01.00.5E.82.22 (hexadecimal)”.

The IGMP message packet consists of, as shown in FIG. 7, a MAC header(14 bytes), an IP header (20 bytes, no option), an IGMP message (8bytes), and a FCS (Flag Check Sequence).

The IP header consists of, as shown in FIG. 8, Version, Header Length(IHL), Type of Service, Packet Length (Total Length), Identification,Flags, Fragment Offset, Time to Live, Protocol, Header Checksum, SourceIP Address (Source Address), Destination IP Address (DestinationAddress), Options, Padding.

The Version consists of 4 bits and indicates a version number of the IPheader. The Header Length (IHL) consists of 4 bits and indicates a sizeof the IP header itself. The Service Type consists of 8 bits andindicates service quality of the transmitted IP. The Packet Lengthconsists of 16 bits and indicates an octet length of an entire packetobtained by adding the IP header and IP data thereto. The Identificationconsists of 16 bits and is used as reference information when data istransferred to a upper layer. The Flags consists of 3 bits and indicatesan instruction to control a division of the packet. The Fragment Offsetconsists of 13 bits and indicates at which part of an original data eachdivided fragment is positioned.

The Time to Live consists of 8 bits and indicates a time when the packetmay exist on the network in units of second. The Protocol consists of 8bits and indicates a protocol in the upper layer. The Header Checksumconsists of 16 bits and indicates a checksum for the IP header.

The Source IP Address consists of 32 bits and indicates an IP address ofthe source. The Destination IP Address consists of 32 bits and indicatesan IP address of the destination. The Options has a variable length andis used for cases such as a security label, a source route, a routerecord, and a time stamp. The Padding is used, when the Options is addedand if the header does not become an integral multiple of 32 bits, ascovering the deficit.

The IGMP Version 1 message consists of, as shown in FIG. 9, Version,Type, Unused, Checksum, and Group Address. The Version consists of 4bits and indicates Version 1 in RFC 1112. The Type consists of 4 bitsand indicates a type of IGMP message. Namely, “1” indicates a query and“2” indicates Report. The Unused consists of 8 bits and indicates zero(0). The Checksum consists of 16 bits and indicates a checksum computedin the same method as that of ICMP. The Group Address consists of 32bits and indicates zero when the message is a query and also an addressof a multicast group of which a host device is to be a member when themessage is a report.

The IGMP Version 2 message consists of, as shown in FIG. 10, 8-bit Type,8-bit Max Response Time (Max Resp Time), Checksum, and Group Addresswithout Version therein. In Version 2, Max Response Time is inserted.This Max Response Time indicates a temporary time for transmitting onlya first piece of Report for each multicast address among Reportsreceived from each port to the multicast router.

The MAC header consists of, as shown in FIG. 11, a destination addressfield for inserting therein a destination MAC address (6 bytes), asource address field for inserting therein a source MAC address (6bytes), and a type field for inserting therein a protocol type (2bytes).

The ping packet consists of, as shown in FIG. 12, a MAC header (4bytes), an IP header (20 bytes, no Options), an ICMP (Internet ControlMessage Protocol) message, and FCS.

Next description is made for an operation. FIG. 13 is a flow chart forexplaining a main operation of the communication control unit. In theconfiguration in FIG. 3, when a packet is received by the port 101 (stepS1), it is determined in the unicast-broadcast/multicast packetdetermining section 201 whether the packet is a unicast/broadcast packetor a multicast packet (step S2). A method of determination is performedbased on a physical address of a multicast packet. Namely, the MACaddress is as shown in FIG. 6, and determination can be made only byconfirming that the address is “0000 0001” in 8 bits from the headerthereof, which can rapidly be determined by processing in the hardware.

When it is determined that the packet is not a multicast packet (stepS2), the packet is transferred by the ordinary LAN switching function(step S3). Namely, the packet is sent to the switching hub section 105from the unicast-broadcast/multicast packet switching section 202, andis subjected therein to forwarding processing for an ordinaryunicast/broadcast packet by referring to the port number-unicast addresscorrelation stored table 106.

On the other hand, when it is determined that the packet is a multicastpacket (step S2), it is confirmed whether the multicast packet ismulticast data or an IGMP message packet (step S4). For theconfirmation, the multicast packet is sent to the IGMP messagedetermining/processing section 203. The IGMP message packet has theformat as shown in FIG. 7, and it is determined by confirming that theprotocol field in the IP header shown in FIG. 8 is “2”. In this case,high-speed determination can be made by processing in the hardware.

Then, when it is determined that the multicast packet is not an IGMPmessage packet (step S4), the received packet is transferred to the portfor connecting thereto a host device as a member of a multicast group aswell as other communication control unit by referring to the portnumber-multicast physical address correlation stored table 206 (stepS5). On the other hand, when it is determined that the multicast packetis an IGMP message packet (step S4), it is checked in the followingsteps of step S6, step S8, and step S10 which type the IGMP message is.

There are two types of version here: Version 1 shown in FIG. 9 andVersion 2 shown in FIG. 10. When host devices or multicast routerssupporting IGMP Version 1 and IGMP Version 2 exist together with eachother, as defined as a function of the IGMP Version 2, an IGMP Version2-supporting multicast router is defined so that the router canunderstand a message based on the IGMP Version 1 and perform processingfor that. For this reason, there occurs no problems if the IGMP Version1 and IGMP Version 2 exist together with each other.

Included in the IGMP are a query and a group specific query each as amessage transmitted by a multicast router, and a report transmitted by ahost device, and further there is leave transmitted by a host device inthe IGMP Version 2. Those messages can be differentiated from each otherby referring to the type field in the IGMP message. When the operationis performed based on the IGMP Version 1, each type field of a query anda group specific query is 0001 (binary), and the type field of a reportis 0010 (binary).

When the operation is performed based on the IGMP Version 2, each typefield of a query and a group specific query is 00010001 (0x11), the typefield of a report is 00010110 (0x16), the type field of leave is00010111 (0x17), and the type field of a report for compatibility withIGMP Version 1 is 00010010 (0x12). As described above, it is understoodthat the above type field is the same as 00010010 obtained by adding theversion field of Report based on the IGMP Version 1 to the type fieldthereof.

Discrimination between a query and a group specific query can be made,because a destination IP address in a query is 224. 0.0.1, namely theMAC address is 01:00:5E:00:00:01 and a group specific query istransmitted to a particular multicast group, as to whether each queryhas any multicast MAC address other than the addresses described aboveor not. By referring to those bit arrays, each message can bediscriminated between IGMP Version 1 and IGMP Version 2, and thisprocessing can rapidly be performed in the hardware. As for any messagenot corresponding to the bit arrays described above, the message isdeleted with no processing subjected thereto as defined in the standard.

When it is determined that the IGMP packet is a query according to themethod of the determination described above (step S6), the port numberhaving received the packet is regarded as being connected to a multicastrouter and registered in the multicast router-connected port numberstored table 209, and the received packet is transmitted to all otherports (step S7).

When it is determined that the IGMP packet is a report (step S8), themulticast physical address of the packet is correlated to a receivingport, and the correlation is registered in the port number-multicastphysical address correlation stored table 206. Then, the received packetis transmitted to the multicast router-connected port by referring tothe multicast router-connected port number stored table 209 (step S9).

When it is determined that the IGMP packet is leave (step S10), acorrelation between the multicast physical address of the packet and areceiving port is retrieved from the port number-multicast physicaladdress correlation stored table 206, and the corresponding correlationis deleted. Then, the received packet is transmitted to the multicastrouter-connected port by referring to the multicast router-connectedport number stored table 209 (step S11).

When it is determined that the IGMP packet does not correspond to any ofa query, a report, and leave (step S10), the received packet is regardedas an unclear IGMP packet to be transmitted to all other ports (stepS12).

Next description is made for a concrete example of the operation when aquery is received by any port connected to the communication controlunit 1A or 1B. FIG. 14 is a flow chart for explaining the operation atthe time of receiving the query. When a packet on a query is received bya port, the received packet is transmitted to all other ports asdescribed above. Then, the Max Response Time included in the querypacket is set in the report control timer 110, and the report controltimer 110 is actuated (step S21).

When measurement by the report control timer 110 is completed, namelywhen it is checked that the Max Response Time is elapsed (step S22), andif it has been completed (elapsed), the processing is ended, and if ithas not been completed (not yet elapsed), existence of the port havingreceived report after receiving a query is checked (step S23). As aresult, if any port having received Report can not be checked (stepS23), the processing returns again to step S22. On the other hand, whena report is received by a port (step S23), it is determined whether thereport has the same destination as that of the multicast address of theReport having been received after a query has been received or not (stepS24).

As a result, when it is determined that the report has a destinationdifferent from that of the report having already been received (stepS24), the multicast physical address of the received packet iscorrelated to the port having received the received packet, and thecorrelation is registered in the port number-multicast physical addresscorrelation stored table 206.

The received packet is transmitted to the multicast router by referringto the multicast router-connected port number stored table 209 (stepS26). Then, the processing returns to step S22. On the other hand, whenit is determined that the report has the same destination as that of theReport having already been received (step S24), the received packetshould be disposed, because the reports may repeatedly be transmitted tothe multicast router, to avoid the repetition in the operation (stepS25). Then, the processing returns to step S22.

With the embodiment from description above, a unicast/broadcast packetis discriminated from a multicast packet, and further the multicastpacket is discriminated from an IGMP message packet, and if a query isdetermined as a result of the discrimination, there are realizedoperations of storing the port number having received the packet and thesource address of the query packet in the multicast router-connectedport number stored table 209 as an address of the multicast router, andalso transmitting the data to ports other than the port having receivedthe query.

With those operations, when the query is received by all the hostdevices or by other routers, or when the plurality of multicast routers11, 12 in FIG. 1 are connected to the subnet SN, it is possible torealize an operation of IGMP that the query is received by both of themulticast routers 11, 12 and that determination can be made which of therouters transmits the query in the subnet SN.

As in the subnet SN, for example, when a plurality of multicast routers11, 12 are connected thereto, it is possible to ensure operations thatany of the multicast routers having the smallest address among thequeries each received by the routers is decided to be a multicast routerfor constantly and periodically transmitting a query, while the othermulticast routers receive the query, and if the query is not received,it is determined that the multicast router is down, so that a multicastrouter having the second smallest IP address is decided to be a routerfor periodically transmitting a query.

As any of the multicast routers 11, 12 transmits a query once, all themulticast routers are stored in the multicast router-connected portnumber stored table 209, but if it is found out that any of themulticast routers 11, 12 is down or is removed from the subnet SN, theentry of the corresponding multicast router can be deleted from themulticast router-connected port number stored table 209.

For this reason, a source address (address of a multicast router) of aquery message as an interface address of the multicast router isconcurrently stored when the query is received, and a ping is alsotransmitted to the multicast router having received the query once bythe ping processing section 112, and if a response to the ping does notreturn, the address entry of the multicast router can automaticallydeleted from the multicast router-connected port number stored table209.

It should be noted that the contents stored in the multicastrouter-connected port number stored table 209 can manually be writtentherein or deleted therefrom through an external device connected to theexternal terminal interface 109.

When Report is received by a port, a destination multicast MAC addressof the packet and a port number having received the packet are stored inthe port number-multicast physical address correlation stored table 206,and are also transferred to the ports stored in the multicastrouter-connected port number stored table 209. When data having thestored multicast address is inputted in a switching hub, a port numberrequiring transfer of the multicast data is obtained by referring to thecontents stored in the port number-multicast physical addresscorrelation stored table 206, so that it is possible to transfer thedata only to a required port.

As for functions of the IGMP, a host device having received Report forthe same multicast group executes an operation that the host device doesnot transfer the Report by its own, and in this case, transferring themulticast packet to the port to which the host device is connected cannot be stored in the switching hub, so that the host device can transferthe packet only to the multicast router connected port stored in themulticast router-connected port number stored table 209 and transfer thereport message only to the multicast router.

The contents stored in the port number-multicast physical addresscorrelation stored table 206 can be written therein or deleted therefromthrough an external device connected to the external terminal interface109.

When leave is received by a port in a switching hub, the leave may bereceived only by a multicast router in the first place. Therefore, thepacket on the leave may be transmitted only to a multicast routerconnected port stored in the multicast router-connected port numberstored table 209.

In addition, if the received packet is sent to the IGMP Leave messageprocessing section 104, an IP multicast address included in the leavemessage therein is extracted, and the extracted address is converted toa multicast MAC address in the multicast physical address generatingsection 204, and if it is found that a correlation between thecorresponding port number and multicast MAC address is stored in theport number-multicast physical address correlation stored table 206, itcan be programmed to delete the correlation therefrom and not totransmit the data for the multicast address to the port having receivedthe leave.

As for the extraction of an IP multicast address and conversion thereofto a multicast physical address, the IGMP packet format and the addressmapping method are defined as shown in FIG. 6, FIG. 9 and FIG. 10, sothat high-speed processing is capable by hardware.

In addition, the following modification may be considered. When leave isreceived, in order to make transfer processing of the Leave faster, theleave is not transmitted only to the multicast router connected portstored in the multicast router-connected port number stored table 209,but may quickly be transmitted to all the ports other than that havingreceived the Leave by omitting the processing of referring to the table.Even if the packet is transmitted to a port not requiring it, the packethas a small amount of data, and the IP address of Leave isALL-ROUTERS-GROUP (224.0.0.2), so that the packet received thereby isignored, and the port is hardly affected.

When a group specific query is received, the group specific query istransmitted to the multicast address of the Leave transmittedimmediately before this transmission. For this reason, it is detected bythe IGMP message determining/processing section 203 that the packet is agroup specific query, and then if it is found that there is any portstored in the port number-multicast physical address correlation storedtable 206 in correlation to the multicast MAC address to which the groupspecific query is transmitted, the packet is transmitted only to theport and also it can be transferred to ports stored in the multicastrouter-connected port number stored table 209 other than the port havingreceived the packet.

In addition, the following modification may be considered. When a groupspecific query is received, in order to make transfer processing of thegroup specific query faster, the group specific query is not transmittedonly to the corresponding port stored in the port number-multicastphysical address correlation stored table 206 in correlation to themulticast MAC address to which the group specify query is transmitted aswell as to the port stored in the multicast router-connected port numberstored table 209, but may quickly be transmitted to all the ports otherthan that having received the group specific query by omitting theprocessing of referring to the table.

Even if the packet is transmitted to a port not requiring it, the packetof the group specific query has a small amount of data, and if a hostdevice connected to the port does not require reception of the packetwith a destination of a multicast address, the packet is ignored, sothat even if the packet is ignored by the host device not requiring it,the port is hardly affected.

Also, the following modification may be considered. As for the operationof IGMP, a host device receiving a query periodically transmitted by amulticast router transmits, when the host device becomes a member of amulticast group to receive multicast data, a report as a response, butdoes not need to transfer the multicast data to the port with the hostdevice connected thereto, for example, when the application isterminated without transmission of leave used when a host device is toleave a group, or when the power is cut off.

For this reason, when a query is received from a multicast routerconnected port, a timer is set for each correlation stored in the portnumber-multicast physical address correlation stored table 206 using thetable entry timer 111, and if a report is not received from each of theports until each timer ends up, a correlation between the multicastphysical address and the port number is deleted, and transfer of amulticast packet to the port can be stopped.

When reception of Report and Leave is checked in the IGMP messagedetermining/processing section 203 in the communication control units 1Aand 1B, the IGMP packet is sent to an external device connected to theexternal terminal interface 109, and the external device can update thecontents of the port number-multicast physical address correlationstored table 206.

In this case, at least sections of the multicast packet processingsection 102 as well as of the report control timer 110 are provided alsoin the external device, and if the contents of the port number-multicastphysical address correlation stored table 206 is updated, the externaldevice updates the contents of the port number-multicast physicaladdress correlation stored table 206, and can perform forwarding of adata packet according to the updated contents.

With this feature, registration of reception of a report to the portnumber-multicast physical address correlation stored table 206 and aload of a function of deleting the corresponding port as well as themulticast MAC address from the port number-multicast physical addresscorrelation stored table 206 by receiving a leave message can reduceinfluence over the switching function for data packet as an originalfunction of the switching hub.

There is also considered a modification that targets high speed packetforwarding by omitting a part of the sequence of checking an IGMPmessage. An IGMP message transmitted from a port stored as a multicastrouter connected port by having received a query to a particular group(other than the address of ALL-ROUTERS-GROUP or ALL-SYSTEMS-GROUP) towhich the multicast router belongs is only the group specific querytransmitted by one of the ports in response to reception of a leavemessage to the address of ALL-ROUTERS-GROUP transmitted by a hostdevice. It is clear from the fact described above that a packet receivedby multicast connected ports is only multicast data to a particulargroup or a query until Leave is received by one of the ports.

For this reason, until a leave message having a multicast MAC addressexisting in the port number-multicast physical address correlationstored table 206 is received by one of the ports, a multicast packetreceived by a port stored as a multicast router connected port is onlychecked with contents of the port number-multicast physical addresscorrelation stored table 206 and determining processing whether thepacket is an IGMP message or not is omitted.

Then, the received packet is forwarded in the same manner as that forordinary unicast data by being transmitted to a port correlated to thesame multicast physical address as that of the packet, which allowsforwarding processing of a multicast packet to be made faster.

In addition, the following modification may be considered. In thecommunication control units 1A and 1B, a multicast packet received by aport other than a multicast router connected port is a multicast packettransmitted by a host device, a report or leave in the IGMP.Accordingly, for the purpose of reducing a load to the processing in theswitching hub as well as of making the forwarding processing of a datapacket faster, a packet having a multicast MAC address received by aport other than the multicast router connected port of a switching hubmay be transmitted to all the multicast router connected ports withoutexecuting processing whether the packet is an IGMP message or not.

The following modification may also be considered. A packet having amulticast address transmitted through a multicast router connected portincludes messages for a multicast routing protocol such as PIM (ProtocolIndependent Multicast) and DVMRP (Distance Vector Multicast RoutingProtocol) other than the IGMP message packet and multicast packet.

For example, each of these messages is, in some cases, transmitted to“ALL-PIM-ROUTERS GROUP (224.0.0.3)” and “DVMRP ROUTERS GROUP(224.0.0.4)” based on a multicast in addition to an adjacent routerbased on a unicast, so that a multicast packet received by a routerconnected port may be transmitted to other port stored in the multicastrouter-connected port number stored table without fail in order toensure the operation of the multicast routing protocol on the networkcomprising a plurality of multicast routers and a plurality of switchinghubs.

It can be found out in the port having received Report that data withwhich multicast address the host device connected thereto desires.However, when a subnet comprises a large number of communication controlunits, and when host devices desiring reception of multicast data areconnected to a large number of ports in each of the communicationcontrol units, the number of reports transmitted from all the hostdevices become large to be overlapped.

Then, when a query message transmitted by a multicast router isreceived, the IGMP message determining/processing section 203 reads aMax Response Time value set inside the query, actuates the reportcontrol timer 110 set in a Max Response Time second at the time ofreceiving the query, transmits only each first report for each multicastaddress among reports received from ports to a multicast routerconnected port until the timer ends up, and disposes the remainingreports. With those operations, it is possible to avoid repetition oftransmitting a report to the multicast router.

The following modification may also be considered. An IGMP message canbe checked with the fact that the protocol field of an IP header is “2”,but, when a type field of an IGMP message is an unknown value and thetype thereof can not be determined, the message may be transferred toall the ports other than the port having received the message based onthe idea that the determination is left to the host devices belonging toa communication control unit and multicast routers.

The following modification may also be considered. An unknown IGMP typevalue may be disposed at a stage when the message is received in thecommunication control units 1A and 1B.

Although the present invention has been described with respect tospecific embodiments for a complete and clear disclosure, the appendedclaims are not be thus limited but are to be construed as embodying allmodifications and alternative constructions that may occur to oneskilled in the art which fairly fail within the basic teaching hereinset forth.

As described above, with the present invention, when it is determinedthat the received packet is a packet on a multicast as well as multicastgroup management protocol, a table showing a correlation between thehost devices and multicast groups is constructed according to thereceived packet, and packet transfer for each multicast group betweenthe multicast router and host devices is controlled according to thetable, so that a multicast packet can be multicast-transferred only torequired host devices with the existing protocol and networkconstruction, and with this feature, it is possible to obtain acommunication control unit which can realize efficient transfer formulticast as well as unicast data transfer.

With the present invention, when it is determined that the packet on themulticast as well as multicast group management protocol is a query, theport having received the packet on a query among a plurality of ports isregistered in the table as a port to which the multicast router isconnected, so that it is possible to obtain a communication control unitwhich can update a correlation between a port and a multicast router asrequired according to contents of the packet.

With the present invention, when a packet on a query is received, it iscontrolled to transfer the packet to all the ports other than the porthaving received the received packet among the plurality of ports, sothat it is possible to obtain a communication control unit which cansurely transfer a query to devices under controls by a multicast router.

With the present invention, a ping is periodically transferred to theport to which the multicast router is connected among the plurality ofports by referring to the table, and when there is any port that doesnot respond to the ping, the correlation between the port and themulticast router is deleted from the table, so that it is possible toobtain a communication control unit which can update disappearance of acorrelation between a multicast router and a port as required accordingto contents of the packet.

With the present invention, when it is determined that a packet on themulticast as well as multicast group management protocol is a report,the port having received the packet on a report among the plurality ofports is registered in the table as a connecting port used when the hostdevice connected to the port is to be a member of an arbitrary multicastgroup, so that it is possible to obtain a communication control unitwhich can update generation of a correlation between a port and a hostdevice for each multicast group as required according to contents of thepacket.

With the present invention, when a packet on a report is received, thepacket on a report is controlled to transfer only to the port to whichthe multicast router is connected by referring to the table, so that itis possible to obtain a communication control unit which can surelytransfer a report from a host device to a multicast router.

With the present invention, when it is determined that a packet on themulticast as well as multicast group management protocol is Leave, theport having received the packet on leave among the plurality of ports isdeleted from the table regarding as a connecting port used when the hostdevice connected to the port leaves an arbitrary multicast group, sothat it is possible to obtain a communication control unit which canupdate disappearance of a correlation between a port and a host devicefor each multicast group as required according to contents of thepacket.

With the present invention, when a packet on leave is received, thepacket on leave is controlled to transfer only to the port to which themulticast router is connected by referring to the table, so that it ispossible to obtain a communication control unit which can surelytransfer leave from a host device to a multicast router.

With the present invention, when a packet on leave is received, thepacket on leave is controlled to transfer to all the ports other thanthe port having received the packet on leave among the plurality ofports, so that the need for processing of searching a port to which themulticast router is connected is eliminated, and with this feature, itis possible to obtain a communication control unit which can make lowspeed processing of leave faster by reducing a load to the processing atthe time of leave operation.

With the present invention, when a packet on a group specific query forchecking that there is no host device being a member of a multicastgroup is received, the packet on a group specific query is controlled totransfer, by referring to the table, to ports each to which a multicastrouter is connected other than the port connecting thereto the hostdevice having been a member of a multicast group as well as the porthaving received the packet on a group specific query, so that the groupspecific query does not need to be broadcast, and with this feature, itis possible to obtain a communication control unit which can efficientlycheck that there is no host device having been a member of a multicastgroup.

With the present invention, when a packet on a group specific query isreceived, the packet on a group specific query is controlled to transferto all the ports other than the port having received the packet on agroup specific query among the plurality of ports, so that the need forprocessing of searching a port to which the multicast router isconnected is eliminated, and with this feature, it is possible to obtaina communication control unit which can make processing of transferringthe group specific query faster by reducing a load to the processing atthe time of group specific query operation.

With the present invention, when there is any port from which Report isnot responded within a specified period of time after the packet on aquery is received, the correlation between the port and the host deviceis deleted from the table, so that it is possible to update informationthat becomes nothing to do with multicast packet transfer as required,and with this feature, it is possible to obtain a communication controlunit which can efficiently execute the processing.

With the present invention, an update operation of the table is executedunder controls by the external device, so that it is possible to obtaina communication control unit which can reduce a load to thecommunication control unit itself.

With the present invention, when a packet is received by a portconnected to the multicast router, and if the received packet is amulticast packet, the received packet is transferred to the host devicesbelonging to the multicast group by referring to the table, so that asequence of checking the multicast group management protocol can beomitted, and with this feature, it is possible to obtain a communicationcontrol unit which can make forwarding of a multicast packet faster.

With the present invention, when a packet is received by a portconnected to a host device belonging to a multicast group stored in thetable, and if the received packet is a multicast packet, the receivedpacket is transferred to the multicast router belonging to the multicastgroup by referring to the table, so that a sequence of checking themulticast group management protocol can be omitted, and with thisfeature, it is possible to obtain a communication control unit which canmake forwarding of a multicast packet faster.

With the present invention, when a packet is received by a port to whichthe router is connected, and if the received packet is a multicastpacket, the received packet is transferred to the multicast router byreferring to the table, so that it is possible to obtain a communicationcontrol unit which can ensure the operation of a multicast routingprotocol on the network comprising a plurality of multicast routers anda plurality of switching hubs.

With the present invention, when a packet on the multicast as well asmulticast group management protocol is a query to ask a host device tobecome a member of a multicast group, only a first Report in eachmulticast group among reports each having a desire to become a member ofa multicast group received by each of the ports is transferred to acorresponding port to which the multicast router is connected byreferring the table during the specified period of time preset insidethe query, and the following Reports are disposed after the specifiedperiod of time is elapsed, so that it is possible to obtain acommunication control unit which can avoid repetition of transmittingReport to a multicast router even on a network in which the subnetcomprises a large number of switching hubs and host devices desiringreception of multicast data are connected to a large number of ports ofeach of the switching hubs.

With the present invention 7, even when it is determined that thereceived packet is a packet on the multicast as well as multicast groupmanagement protocol, but if the received packet does not correspond atleast to any type of a query to ask a host device to become a member ofa multicast group, a report that a host device desires to be a member ofa multicast group, and of leave indicating that a host device desires toleave a multicast group, the received packet is transferred to all theplurality of ports, so that it is possible to obtain a communicationcontrol unit which can leave the determination to each device as adestination to which the packet is transferred when it can not bedetermined which type a multicast packet corresponds to.

With the present invention, even when it is determined that the receivedpacket is a packet on the multicast as well as multicast groupmanagement protocol, but if the received packet does not correspond atleast to any type of a query to ask a host device to become a member ofa multicast group, a report that a host device desires to be a member ofa multicast group, and of Leave indicating that a host device desires toleave a multicast group, the received packet is disposed, so that it ispossible to obtain a communication control unit which can clear off anunclear type of multicast packet from a network and can enhanceefficiency of ordinary multicast packet transfer.

With the present invention, there are steps of determining contents of areceived packet, and constructing, when it is determined that thereceived packet is a packet on the multicast as well as multicast groupmanagement protocol, a table showing a correlation between the hostdevices and multicast groups for controlling a path of a multicastpacket according to the received packet, so that it is possible toobtain a communication control method applied for a multicast-supportingLAN which can maintain conditions to control multicast-transfer of amulticast packet only to required host devices with the existingprotocol and network construction inside the packet.

With the present invention, there is also a step of transferring, when amulticast packet is received from a multicast router, a packet for eachmulticast group between the multicast router and host devices accordingto the table showing a correlation between host devices and multicastgroups, so that a multicast packet can be multicast-transferred only torequired host devices with the existing protocol and networkconstruction, and with this feature, it is possible to obtain acommunication control method applied for a multicast-supporting LANwhich can realize efficient transfer for multicast as well as unicastdata transfer.

This application is based on Japanese patent application No. HEI10-170339 filed in the Japanese Patent Office on Jun. 17, 1998, theentire contents of which are hereby incorporated by reference.

Although the invention has been described with respect to a specificembodiment for a complete and clear disclosure, the appended claims arenot to be thus limited but are to be construed as embodying allmodifications and alternative constructions that may occur to oneskilled in the art which fairly fall within the basic teaching hereinset forth.

What is claimed is:
 1. A switch for transmitting a packet in a network,comprising: a first port to receive a first packet; a table to include afirst correlation information between a multicast group and a port towhich a host device belonging to the multicast group is coupled; and aprocessor to determine that the received first packet from the firstport is a first message packet that has been transmitted under amulticast group management protocol to inform that a first host devicecoupled to the first port desires to leave a multicast group to whichthe first host device belongs, and wherein the first correlationinformation is updated when the processor determines that the receivedfirst packet is the first message packet, whether or not the first portis coupled to a host belonging to the multicast group.
 2. A switchaccording to claim 1, wherein the first correlation information betweenthe multicast group to which the first host device belongs and a firstport is deleted when the processor determines that the received firstpacket is the first message packet.
 3. A switch according to claim 1,wherein the first correlation information is based on a multicastphysical address of the multicast group.
 4. A switch according to claim1, wherein the table includes a second correlation information between amulticast router and a port to which the multicast router is coupled. 5.A switch according to claim 4, wherein the second correlationinformation is based on a physical address of the multicast router.